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Cassini finds football-field sized moonlets at Saturn CORNELL UNIVERSITY NEWS RELEASE Posted: March 29, 2006 New observations of propeller-shaped disturbances in Saturn's A ring indicate the presence of four small, embedded moons -- and most likely millions more, Cornell University astronomers report.
Matthew Tiscareno, a Cornell research associate, is lead author of a paper describing the discovery in the March 30 issue of the journal Nature. The four disturbances, which appear as pairs of slightly offset bright horizontal streaks in an otherwise bland region of the ring, were captured in two images taken in 2004 by NASA's Cassini spacecraft. Astronomers say the streaks are indicators of orbiting moons about 100 meters (328 feet) in diameter: about the length of a football field, but still too small for even Cassini's highly sensitive Imaging Science Subsystem (ISS) to see directly, but large enough to exert an observable gravitational pull on the particles around them. "The discovery of these intermediate-sized particles tells us that Pan and Daphnis are probably just the largest members of the ring population, rather than interlopers from somewhere else," said Tiscareno. A continuum of particle sizes lends strong support to the theory that Saturn's rings were formed when another object fragmented close to the planet, breaking into pieces which were then captured by Saturn's gravitational pull. "There has always been the question about whether the rings were primordial material that was unable to grow into a moon or debris left over from a breakup event," said Joseph Burns, Cornell professor of astronomy and of theoretical and applied mechanics and paper co-author, along with Cornell research associate Matthew Hedman and researchers at other institutions. The discovery doesn't rule out the accretion model, but "it's a step in that direction," said Tiscareno. "It's hard for direct accretion to produce particles this large. It's much easier if you start with a solid icy core, like a shard from a breakup."
Like a motorboat's wake on a smooth lake, the four observed disturbances are particularly visible since the area they inhabit is otherwise smooth. But the fact that four were found in just two images covering only a tiny fraction of the ring makes it likely that millions more exist. By studying them further, researchers hope to gain a better understanding of how Saturn's rings formed -- and even about how solar systems form around stars. "The structures we observe with Cassini are strikingly similar to those seen in many numerical models of the early stages of planetary formation, even though the scales are vastly different," said Carl Murray, a co-author and astronomer at Queen Mary College, University of London. "In this way, Cassini is giving us unique insight into the origin of planets." The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology, manages the mission for NASA. During its Saturn tour, as currently planned, Cassini will complete 74 orbits of the ringed planet, 44 close flybys of the moon Titan and numerous flybys of Saturn's other icy moons. |
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A total solar eclipse occurred March 29. This video from Side, Turkey shows the period of totality when the moon slid between the Earth and Sun. The eclipse revealed the Sun's glowing outer halo of million-degree gas, called the solar corona.
In early March, NASA cancelled its Dawn mission built to orbit two of the solar system's largest asteroids using ion engine propulsion. Technical problems and cost overruns were blamed. But in this news conference from March 27, agency officials announce NASA's decision to reverse the cancellation and restart the mission.
Lockheed Martin holds this news conference in Houston on March 24 to announced that it is partnering with the State of Texas to locate the Crew Exploration Vehicle (CEV) program office in Houston, as well as systems engineering, software development and qualification testing, if the corporation wins the NASA contract to build the next generation spacecraft for NASA.
As the Expedition 12 mission aboard the International Space Station winds down, officials managing the flight from Mission Control in Houston hold this retrospective briefing to talk about the highs and lows, the science, the spacewalks and everything in between.
International Space Station officials preview the next Expedition mission to the orbiting outpost, which is scheduled for launch March 29. The preview was given during a briefing March 22 from Johnson Space Center.
One of the iconic moments of the early space shuttle program was astronaut Bruce McCandless floating above the brilliantly blue Earth completely disconnected from his spacecraft. He was testing the Manned Maneuvering Unit, a jet-powered backpack that would enable spacewalkers to travel away from the space shuttle to service satellites. In this post-flight presentation, the crew of Challenger's STS-41B mission of February 1984 narrate the film highlights from their mission that also included the first shuttle landing at Kennedy Space Center.
